I have taken Keppra for a number of years, I have not gained weight at all. Constipation maybe but drink six to eight glasses of water a day and supplement with an organic psyllium product and constipation should not be an issue. Yes it is difficult to drink 8 glasses of water a day but go to bed early and drink water all day... start early and I prefer room temperature H2O... you don't want to be running all night to pee